Semiconductor device

ABSTRACT

A device includes a substrate, a shallow trench isolation (STI) structure, an isolation structure, and a gate stack. The substrate has a semiconductor fin. The shallow trench isolation (STI) structure is over the substrate and laterally surrounding the semiconductor fin. The isolation structure is disposed on a top surface of the STI structure. The gate stack crosses the semiconductor fin, over the STI structure, and in contact with a sidewall the isolation structure, in which the gate stack includes a high-k dielectric layer extending from a sidewall of the semiconductor fin to the top surface of the STI structure and terminating prior to reaching the sidewall of the isolation structure, and in which the high-k dielectric layer is in contact with the top surface of the STI structure.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.16/716,207, filed Dec. 16, 2019, now U.S. Pat. No. 10,840,379, issuedNov. 17, 2020, which is a continuation of U.S. patent application Ser.No. 16/041,664, filed Jul. 20, 2018, now U.S. Pat. No. 10,510,896,issued Dec. 17, 2019, which is a divisional of U.S. patent applicationSer. No. 14/887,873, filed Oct. 20, 2015, now U.S. Pat. No. 10,032,914,issued Jul. 24, 2018, which are herein incorporated by reference intheir entireties.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three dimensional designs, such as afin-like field effect transistor (FinFET). A FinFET includes an extendedsemiconductor fin that is elevated above a substrate in a directionnormal to the plane of the substrate. The channel of the FET is formedin this vertical fin. A gate is provided over (e.g., wrapping) the fin.The FinFETs further can reduce the short channel effect.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the presented disclosure are best understood from thefollowing detailed description when read with the accompanying figures.It is noted that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIGS. 1A to 9A are top views of a method for manufacturing asemiconductor device at various stages in accordance with someembodiments of the presented disclosure.

FIGS. 1B to 9B are cross-sectional views respectively taking along lineB-B of FIGS. 1A to 9A.

FIGS. 10A to 12A are top views of a method for manufacturing asemiconductor device at various stages in accordance with someembodiments of the presented disclosure.

FIGS. 10B to 12B are cross-sectional views respectively taking alongline B-B of FIGS. 11A to 12A.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the presented disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the presented disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Embodiments of the presented disclosure provide some improved methodsfor the formation of semiconductor devices and the resulting structures.These embodiments are discussed below in the context of forming finFETtransistors having a single fin or multiple fins on a bulk siliconsubstrate. One of ordinary skill in the art will realize thatembodiments of the presented disclosure may be used with otherconfigurations.

FIGS. 1A to 9A are top views of a method for manufacturing asemiconductor device at various stages in accordance with someembodiments of the presented disclosure, and FIGS. 1B to 9B arecross-sectional views respectively taking along line B-B of FIGS. 1A to9A. Reference is made to FIGS. 1A and 1B. A substrate 110 is provided.The substrate 110 includes a semiconductor fin 112 protruded from a topsurface 111 of the substrate 110. In some embodiments, the semiconductorfin 112 includes silicon. It is note that the numbers of thesemiconductor fin 112 in FIGS. 1A and 1B are illustrative, and shouldnot limit the claimed scope of the presented disclosure. A person havingordinary skill in the art may select suitable numbers for thesemiconductor fin 112 according to actual situations.

In some embodiments, the substrate 110 may be a semiconductor materialand may include known structures including a graded layer or a buriedoxide, for example. In some embodiments, the substrate 110 includes bulksilicon that may be undoped or doped (e.g., p-type, n-type, or acombination thereof). Other materials that are suitable forsemiconductor device formation may be used. Other materials, such asgermanium, quartz, sapphire, and glass could alternatively be used forthe substrate 110. Alternatively, the silicon substrate 110 may be anactive layer of a semiconductor-on-insulator (SOI) substrate or amulti-layered structure such as a silicon-germanium layer formed on abulk silicon layer.

The semiconductor fin 112 may be formed, for example, by patterning andetching the substrate 110 using photolithography techniques. In someembodiments, a layer of photoresist material (not shown) is depositedover the substrate 110. The layer of photoresist material is irradiated(exposed) in accordance with a desired pattern (the semiconductor fin112 in this case) and developed to remove a portion of the photoresistmaterial. The remaining photoresist material protects the underlyingmaterial from subsequent processing steps, such as etching. It should benoted that other masks, such as an oxide or silicon nitride mask, mayalso be used in the etching process.

In some other embodiments, the semiconductor fin 112 may be epitaxiallygrown. For example, exposed portions of an underlying material, such asan exposed portion of the substrate 110, may be used in an epitaxialprocess to form the semiconductor fin 112. A mask may be used to controlthe shape of the semiconductor fin 112 during the epitaxial growthprocess.

In FIG. 1B, a plurality of isolation structures 114 are formed on thesubstrate 110 and adjacent to the semiconductor fin 112. The isolationstructures 114, which act as a shallow trench isolation (STI) around thesemiconductor fin 112, may be formed by chemical vapor deposition (CVD)techniques using tetra-ethyl-ortho-silicate (TEOS) and oxygen as aprecursor. In some other embodiments, the isolation structures 114 maybe formed by implanting ions, such as oxygen, nitrogen, carbon, or thelike, into the substrate 110. In yet some other embodiments, theisolation structures 114 are insulator layers of a SOI wafer.

In FIG. 1B, a gate insulating film 120 is formed on the semiconductorfin 112. The gate insulating film 120, which prevents electrondepletion, may include, for example, a high-k dielectric material suchas metal oxides, metal nitrides, metal silicates, transitionmetal-oxides, transition metal-nitrides, transition metal-silicates,oxynitrides of metals, metal aluminates, zirconium silicate, zirconiumaluminate, or combinations thereof. Some embodiments may include hafniumoxide (HfO₂) hafnium silicon oxide (HfSiO), hafnium silicon oxynitride(HfSiON), hafnium tantalum oxide (HfTaO), hafnium titanium oxide(HfTiO), hafnium zirconium oxide (HfZrO), lanthanum oxide (LaO),zirconium oxide (ZrO), titanium oxide (TiO), tantalum oxide (Ta₂O₅),yttrium oxide (Y₂O₃), strontium titanium oxide (SrTiO₃, STO), bariumtitanium oxide (BaTiO₃, BTO), barium zirconium oxide (BaZrO), hafniumlanthanum oxide (HfLaO), lanthanum silicon oxide (LaSiO), aluminumsilicon oxide (AlSiO), aluminum oxide (Al₂O₃), silicon nitride (Si₃N₄),oxynitrides (SiON), and combinations thereof. The gate insulating film120 may have a multilayer structure such as one layer of silicon oxide(e.g., interfacial layer) and another layer of high-k material. The gateinsulating film 120 may have a thickness T ranging from about 10 toabout 30 angstroms (Å). The gate insulating film 120 may be formed usingCVD, physical vapor deposition (PVD), atomic layer deposition (ALD),thermal oxide, ozone oxidation, other suitable processes, orcombinations thereof.

CVD is a technique of thin solid film deposition on substrates from thevapor species through chemical reactions. The chemical reaction is oneof distinctive features that CVD possesses compared with other filmdeposition techniques such as PVD. A tube-furnace CVD system for mayinclude a gas delivery system, a reactor, and a gas removal system.During the CVD process, reactive gas species are fed into the reactor bythe gas delivery system through valves. A gas-mixing unit may mix thevarious gases before they are let in the reactor. The reactor is wherethe chemical reaction takes place and the solid materials are depositedon substrates as the purpose of the reaction. The heaters are placedsurrounding the reactor to provide high temperatures for the reaction.The by-products of the reaction and non-reacted gases are removed by thegas removal system. PVD is a deposition method which involves physicalprocesses such as a plasma sputter bombardment rather than involving achemical reaction at the surface. In the plasma sputter process, atomsor molecules are ejected from a target material by high-energy particlebombardment so that the ejected atoms or molecules can condense on asubstrate as a thin film. ALD is a gas phase chemical process and it isa self-limiting atomic layer-by-layer growth method. Thesurface-controlled growth mechanism of ALD provides good step coverageand dense films with few (or no) pinholes. The precision achieved withALD allows processing of thin films in a controlled way in the nanometerscale.

In FIGS. 1A and 1B, a dummy layer 130 is formed on the substrate 110 tocover the gate insulating film 120 and the semiconductor fin 112. Inother words, the gate insulating film 120 is disposed between the dummylayer 130 and the semiconductor fin 112 of the substrate 110. In someembodiments, the dummy layer 130 includes a semiconductor material suchas polysilicon, amorphous silicon, or the like. The dummy layer 130 maybe deposited doped or undoped. For example, in some embodiments, thedummy layer 130 includes polysilicon deposited undoped by low-pressurechemical vapor deposition (LPCVD). The polysilicon may also bedeposited, for example, by furnace deposition of an in-situ dopedpolysilicon. Alternatively, the dummy layer 130 may includes othersuitable materials.

In some embodiments, as shown in FIG. 1A, a plurality of gate spacers140 are formed on opposing sides of the dummy layer 130. In someembodiments, at least one of the gate spacers 140 includes single ormultiple layers. The gate spacers 140 can be formed by blanketdepositing one or more dielectric layer(s) (not shown) on the previouslyformed structure. The dielectric layer(s) may include silicon nitride(SiN), oxynitride, silicon carbon (SiC), silicon oxynitride (SiON),oxide, and the like and may be formed by methods utilized to form such alayer, such as CVD, plasma enhanced CVD, sputter, and other methodsknown in the art. The gate spacers 140 may include different materialswith different etch characteristics than the dummy layer 130 so that thegate spacers 140 may be used as masks for the patterning of the dummylayer 130 (described below with references to FIGS. 3A-3B). The gatespacers 140 may then be patterned, such as by one or more etches toremove the portions of the gate spacers 140 from the horizontal surfacesof the structure.

Reference is made to FIGS. 2A and 2B. A mask is formed over the dummylayer 130 and the semiconductor fin 112, and is patterned to form apatterned mask 150, which defines an insulation area between gate stacks105 (see FIGS. 9A and 9B), i.e., to define the ends of the gate stacks105. In some embodiments, the patterned mask 150 is a photoresist maskformed by depositing, exposing, and developing a layer of photoresistmaterial. The patterned mask 150 forms the insulation area between thegate stacks 105 in subsequent processing steps as discussed in greaterdetail below.

Reference is made to FIGS. 3A and 3B. The dummy layer 130 (see FIGS. 2Aand 2B) is partially removed (or patterned) in the regions exposed bythe patterned mask 150 (i.e., the insulation area) by an etching backprocess or other suitable process to form patterned dummy layers 132.For example, the dummy layer 130 may be selectively etched therebyforming a through hole 134 between the gate spacers 140 (see FIG. 3A)and between the patterned dummy layers 132 (see FIG. 3B). The throughhole 134 is laterally separated from the semiconductor fin 112 by adistance D. At least one of the patterned dummy layers 132 covers thesemiconductor fin 112. The portion of the dummy layer 130 exposed by thepatterned mask 150 may be removed by a wet etch process that includesexposure to hydroxide containing solution (e.g., ammonium hydroxide),deionized water, and/or other suitable etchant solutions.

Reference is made to FIGS. 4A and 4B. The patterned mask 150 (see FIGS.3A and 3B) is removed by an ashing, stripping, or other suitabletechnique. Then, an insulating structure 160 is disposed in the throughhole 134. The insulating structure 160 may be a plug which is surroundedby the gate spacers 140 and the patterned dummy layers 132. For example,an inter-layer dielectric (ILD) (not shown) is formed over the patterneddummy layers 132 and in the through hole 134. A chemical mechanicalplanarization (CMP) process may then be performed to etch back andplanarize the ILD to form the insulating structure 160. In someembodiments, the ILD is formed of an oxide such as phospho-silicateglass (PSG), boro-silicate glass (BSG), boron-doped phospho-silicateglass (BPSG), TEOS, or the like.

Reference is made to FIGS. 5A and 5B. For clarity, the gate insulatingfilm 120 is depicted in FIG. 5B and is omitted in FIG. 5A. The patterneddummy layers 132 (see FIGS. 4A and 4B) are removed by an etching backprocess or other suitable process to form openings 136 on opposite sidesof the insulating structure 160 and between the gate spacers 140. One ofthe openings 136 exposes a portion of the gate insulating film 120disposed on the semiconductor fin 112, and a gap G is formed in theopening 136 and between the insulating structure 160 and thesemiconductor fin 112. Furthermore, at least a sidewall 162 of theinsulating structure 160 facing the semiconductor fin 112 and sidewalls142 of the gate spacers 140 are exposed. The gap G has inner surfaces,such as the sidewall 162, the sidewalls 142, and a bottom surface 115.The patterned dummy layers 132 may be removed by a wet etch process thatincludes exposure to hydroxide containing solution (e.g., ammoniumhydroxide), deionized water, and/or other suitable etchant solutions.

It is noted that although in the insulating structure 160 of FIGS. 5Aand 5B is formed according to the manufacturing processes of FIGS. 1A to5B, the claimed scope of the presented disclosure is not limited in thisrespect. In some other embodiments, the insulating structure 160 can beformed by forming an insulating layer on the gate insulating film 120and then patterning it without forming the dummy layer 130 (see FIGS. 1Aand 1B).

Reference is made to FIGS. 6A and 6B. A high dielectric constant(high-κ) dielectric layer 170 is conformally formed in the openings 136.Therefore, the high-κ dielectric layer 170 covers the semiconductor fin112, the bottom surface 115 of the gap G, and the sidewall 162 of theinsulating structure 160 facing the semiconductor fin 112. In addition,the high-κ dielectric layer 170 further covers the sidewalls 142 of thegate spacers 140. In some embodiments, another interfacial layer isdeposited first if the interfacial layer 120 of FIG. 1B is removed in aprevious process step. The high-κ dielectric layer 170 has a dielectricconstant (κ) higher than the dielectric constant of SiO₂, i.e. κ>3.9.The high-κ dielectric layer 170 may include LaO, AlO, ZrO, TiO, Ta₂O₅,Y₂O₃, SrTiO₃ (STO), BaTiO₃ (BTO), BaZrO, HfZrO, HfLaO, HfSiO, LaSiO,AlSiO, HfTaO, HfTiO, (Ba,Sr)TiO₃ (BST), Al₂O₃, Si₃N₄, oxynitrides(SiON), or other suitable materials. The high-κ dielectric layer 170 isdeposited by suitable techniques, such as ALD, CVD, PVD, thermaloxidation, combinations thereof, or other suitable techniques.

Reference is made to FIGS. 7A and 7B. Subsequently, the high-κdielectric layer 170 is partially removed to expose the sidewall 162 ofthe insulating structure 140, a portion of the bottom surface 115 of thegap G, and first portions 143 of the sidewalls 142 of the gate spacers140 while covers second portions 144 of the sidewalls 142 of the gatespacers 140. The first portion 143 of the sidewall 142 of the gatespacer 140 is present adjacent to the sidewall 162 of the insulatingstructure 160 and between the second portion 144 of the gate spacer 140and the insulating structure 160. In other words, the high-κ dielectriclayer 170 is separated from the insulating structure 160. The high-κdielectric layer 170 may be partially removed by etching the high-κdielectric layer 170. The etching process includes dry etch, wet etch,or a combination of dry and wet etch. The etching process may include amultiple-operation etching to gain etch selectivity, flexibility anddesired etch profile.

Reference is made to FIGS. 8A and 8B. A metal layer 180 is conformallyformed in the openings 136 and on the high-κ dielectric layer 170. Inother words, the metal layer 180 covers the high-κ dielectric layer 170.Therefore, the metal layer 180 attaches to the sidewall 162 of theinsulating structure 160, the bottom surface 115 of the gap G, and thefirst portions 143 of the sidewalls 142 of the gate spacers 140. Themetal layer 180 may be a work-function (WF) metal layer. In someembodiments, the WF metal layer can include impurities. For example, theimpurity used in providing an N-type work-function shift is an elementfrom the Lanthanide group. Examples of P-type WF metal layer mayinclude, but not limited to, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, and Pt. Pdcan be used as an impurity in a P-type WF layer. The metal layer 180 maybe formed by depositing WF metal materials in the openings 136. Themetal layer 180 may include a single layer or multi layers, such as a WFlayer, a liner layer, a wetting layer, and an adhesion layer. The metallayer 180 may include Ti, TiAlN, TaC, TaCN, TaSiN, Mn, Zr, TiN, TaN, Ru,Mo, WN, or any suitable materials. The metal layer 180 may be formed byALD, PVD, CVD, or other suitable process.

Reference is made to FIGS. 9A and 9B. A gate electrode 190 is formed onthe metal layer 180 and fills the opening 136. Furthermore, the gateelectrode 190 at least disposed in the gap G between the insulatingstructure 160 and the semiconductor fin 112. The gate electrode 190 mayinclude aluminum (Al), copper (Cu), AlCu, tungsten (W) or other suitableconductive material. The gate electrode 190 is deposited by ALD, PVD,CVD, or other suitable process. With the gate electrode 190, the metallayer 180, and the high-κ dielectric layer 170, a gate stack 105 isformed. In some embodiments, a metal CMP process is applied to removeexcessive the gate electrode 190 to provide a substantially planar topsurface for the gate stack 105, the insulating structure 160, and thegate spacer 140. Hence, the gate stack 105 and the semiconductor fin 112can form a fin field effect transistor (finFET). The process from FIGS.5A to 9B is referred as a replacement gate loop process. Furthermore, ifthe patterned dummy layer 132 of FIGS. 4A and 4B is made of polysilicon,the process from FIGS. 5A to 9B is referred as a replacement polysilicongate (RPG) loop process.

According to the aforementioned embodiments, the insulating structure isdisposed between two adjacent gate stacks to isolate the two adjacentgate stacks. Since at least a portion of the high-κ dielectric layercovering the sidewall of the insulating structure is removed before theformations of the metal layer and the gate electrode, the depositingwindows for the metal layer and the gate electrode is enlarged. Inaddition, the size of the gap between the insulating structure and thesemiconductor fin is also enlarged. Hence, the gate electrode can fillthe gap between the insulating structure and the semiconductor fin,reducing the probability of formation of void therein. With thisconfiguration, the voltage performance of the gate stack can beimproved.

FIGS. 10A to 12A are top views of a method for manufacturing asemiconductor device at various stages in accordance with someembodiments of the presented disclosure, and FIGS. 10B to 12B arecross-sectional views respectively taking along line B-B of FIGS. 10A to12A. The manufacturing processes of FIGS. 1A to 6B are performed inadvance. Since the relevant manufacturing details are similar to theabovementioned embodiments, and, therefore, a description in this regardwill not be repeated hereinafter. Reference is made to FIGS. 10A and10B. A metal layer 180 is conformally formed in the openings 136 and onthe high-κ dielectric layer 170. In other words, the metal layer 180covers the high-κ dielectric layer 170. The metal layer 180 may be awork-function (WF) metal layer. In some embodiments, the WF metal layercan include impurities. For example, the impurity used in providing anN-type work-function shift is an element from the Lanthanide group.Examples of P-type WF metal layer may include, but not limited to, Re,Fe, Ru, Co, Rh, Ir, Ni, Pd, and Pt. Pd can be used as an impurity in aP-type WF layer. The metal layer 180 may be formed by depositing WFmetal materials in the openings 136. The metal layer 180 may include asingle layer or multi layers, such as a WF layer, a liner layer, awetting layer, and an adhesion layer. The metal layer 180 may includeTi, TiAlN, TaC, TaCN, TaSiN, Mn, Zr, TiN, TaN, Ru, Mo, WN, or anysuitable materials. The metal layer 180 may be formed by ALD, PVD, CVD,or other suitable process.

Reference is made to FIGS. 11A and 11B. Subsequently, the high-κdielectric layer 170 and the metal layer 180 are together partiallyremoved to expose the sidewall 162 of the insulating structure 140, aportion of the bottom surface 115 of the gap G, and the first portions143 of the sidewalls 142 of the gate spacers 140 while covers secondportions 144 of the sidewalls 142 of the gate spacers 140. The firstportion 143 of the sidewall 142 of the gate spacer 140 is presentadjacent to the sidewall 162 of the insulating structure 160 and betweenthe second portion 144 of the gate spacer 140 and the insulatingstructure 160. In other words, the high-κ dielectric layer 170 and themetal layer 180 are separated from the insulating structure 160. Thehigh-κ dielectric layer 170 and the metal layer 180 may be partiallyremoved by etching the high-κ dielectric layer 170 and the metal layer180. The etching process includes dry etch, wet etch, or a combinationof dry and wet etch. The etching process may include amultiple-operation etching to gain etch selectivity, flexibility anddesired etch profile.

Reference is made to FIGS. 12A and 12B. A gate electrode 190 is formedon the metal layer 180 and is at least disposed in the opening 136.Therefore, the gate electrode 190 attaches to the sidewall 162 of theinsulating structure 160, the portion of the bottom surface 115 of thegap G, and the first portions 143 of the sidewalls 142 of the gatespacers 140. Furthermore, the gate electrode 190 fills the gap G betweenthe insulating structure 160 and the semiconductor fin 112. The gateelectrode 190 may include aluminum (Al), copper (Cu), AlCu, tungsten (W)or other suitable conductive material. The gate electrode 190 isdeposited by ALD, PVD, CVD, or other suitable process. With the gateelectrode 190, the metal layer 180, and the high-κ dielectric layer 170,a gate stack 105 is formed. In some embodiments, a metal CMP process isapplied to remove excessive the gate electrode 190 to provide asubstantially planar top surface for the gate stack 105, the insulatingstructure 160, and the gate spacer 140. Hence, the gate stack 105 andthe semiconductor fin 112 can form a fin field effect transistor(finFET).

According to the aforementioned embodiments, the insulating structure isdisposed between two adjacent gate stacks to isolate the two adjacentgate stacks. Since at least a portion of the high-κ dielectric layer andat least a portion of the metal layer covering the sidewall of theinsulating structure is removed before the formations of the gateelectrode, the depositing windows for the gate electrode is enlarged. Inaddition, the size of the gap between the insulating structure and thesemiconductor fin is also enlarged. Hence, the gate electrode can fillthe gap between the insulating structure and the semiconductor fin,reducing the probability of formation of void therein. With thisconfiguration, the voltage performance of the gate stack can beimproved.

According to some embodiments, a device includes a substrate, a shallowtrench isolation (STI) structure, an isolation structure, and a gatestack. The substrate has a semiconductor fin. The shallow trenchisolation (STI) structure over the substrate and laterally surroundingthe semiconductor fin. The isolation structure is disposed on a topsurface of the STI structure. The gate stack crosses the semiconductorfin, over the STI structure, and in contact with a sidewall theisolation structure, in which the gate stack includes a high-kdielectric layer extending from a sidewall of the semiconductor fin tothe top surface of the STI structure and terminating prior to reachingthe sidewall of the isolation structure, and in which the high-kdielectric layer is in contact with the top surface of the STIstructure.

According to some embodiments, a device includes a substrate, a gatestructure, an isolation structure, and a spacer. The substrate has asemiconductor fin. The gate structure crosses the semiconductor fin, inwhich the gate structure comprises a high-k dielectric layer, a workfunction metal layer over the high-k dielectric layer, and a gateelectrode over the work function metal layer. The isolation structure isover the substrate and in contact with the gate structure. The spacerextends from a sidewall of the isolation structure to a sidewall of thework function metal layer of the gate structure.

According to some embodiments, a device includes a substrate, a gatestructure, an isolation structure, and a spacer. The substrate has asemiconductor fin. The gate structure crosses the semiconductor fin, inwhich the gate structure comprises a high-k dielectric layer, a workfunction metal layer over the high-k dielectric layer, and a gateelectrode over the work function metal layer. The isolation structure isover the substrate and in contact with the gate structure. The spacer ison a sidewall of the gate structure, in which the work function metallayer of the gate structure is in contact with the spacer and theisolation structure.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presenteddisclosure. Those skilled in the art should appreciate that they mayreadily use the presented disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe presented disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the presented disclosure.

What is claimed is:
 1. A device, comprising: a substrate having asemiconductor fin; a shallow trench isolation (STI) structure over thesubstrate and laterally surrounding the semiconductor fin; an isolationstructure disposed on a top surface of the STI structure; and a gatestack crossing the semiconductor fin, over the STI structure, and incontact with a sidewall the isolation structure, wherein the gate stackcomprises a high-k dielectric layer extending from a sidewall of thesemiconductor fin to the top surface of the STI structure andterminating prior to reaching the sidewall of the isolation structure,and wherein the high-k dielectric layer is in contact with the topsurface of the STI structure.
 2. The device of claim 1, furthercomprising a gate insulating film between the high-k dielectric layerand the semiconductor fin.
 3. The device of claim 1, wherein the gatestack further comprises a metal layer extending over the high-kdielectric layer and terminating prior to reaching the sidewall of theisolation structure.
 4. The device of claim 3, wherein the gate stackfurther comprises a gate electrode over the metal layer and in contactwith the sidewall of the isolation structure.
 5. The device of claim 4,wherein the gate electrode is in contact with the top surface of theisolation structure.
 6. The device of claim 4, wherein the gateelectrode is in contact with an end of the high-k dielectric layer andan end of the metal layer.
 7. The device of claim 1, wherein the gatestack further comprises a metal layer extending along the high-kdielectric layer, the top surface of the STI structure, and the sidewallof the isolation structure.
 8. A device, comprising: a substrate havinga semiconductor fin; a gate structure crossing the semiconductor fin,wherein the gate structure comprises a high-k dielectric layer, a workfunction metal layer over the high-k dielectric layer, and a gateelectrode over the work function metal layer; an isolation structureover the substrate and in contact with the gate structure; and a spacerextending from a sidewall of the isolation structure to a sidewall ofthe work function metal layer of the gate structure.
 9. The device ofclaim 8, wherein a portion of the high-k dielectric layer in contactwith the spacer is laterally between the isolation structure and thehigh-k dielectric layer.
 10. The device of claim 8, wherein the spacerfurther extends to a sidewall of the high-k dielectric layer.
 11. Thedevice of claim 8, wherein the work function metal layer has a steppedsidewall when viewed from above.
 12. The device of claim 8, wherein,when viewed from above, the work function metal layer includes a firstportion in contact with the spacer and a second portion in contact withan inner sidewall of the high-k dielectric layer distal to the spacer.13. The device of claim 12, wherein the work function metal layerfurther includes a third portion in contact with the isolationstructure.
 14. The device of claim 8, further comprising a shallowtrench isolation (STI) structure over the substrate, laterallysurrounding the semiconductor fin, and in contact with the work functionmetal layer.
 15. The device of claim 14, wherein the STI structure isfurther in contact with a bottom surface of the isolation structure andthe high-k dielectric layer.
 16. A device, comprising: a substratehaving a semiconductor fin; a gate structure crossing the semiconductorfin, wherein the gate structure comprises a high-k dielectric layer, awork function metal layer over the high-k dielectric layer, and a gateelectrode over the work function metal layer; an isolation structureover the substrate and in contact with the gate structure; and a spaceron a sidewall of the gate structure, wherein the work function metallayer of the gate structure is in contact with the spacer and theisolation structure.
 17. The device of claim 16, wherein the spacerextend from an outer sidewall of the high-k dielectric layer to an outersidewall of the work function metal layer.
 18. The device of claim 16,further comprising a shallow trench isolation (STI) structure over thesubstrate, laterally surrounding the semiconductor fin, and in contactwith a lateral portion of the high-k dielectric layer.
 19. The device ofclaim 16, wherein a bottommost surface of the work function metal layeris lower than a top surface of the lateral portion of the high-kdielectric layer.
 20. The device of claim 16, wherein the work functionmetal layer is laterally between the high-k dielectric layer and theisolation structure.